Absorptive devices, such as diapers, sanitary napkins, disposable bedpads, incontinent pads, and the like are well known. These device are used to absorb liquid from the human body and retain that liquid, It is also known to cover the exterior of these devices with a flexible, plastic sheet to prevent the liquid absorbed from striking through the absorptive device and soiling other adjacent clothing, such as bedding and wearing apparel. Although such waterproof plastic sheets of the prior art are highly effective in preventing strikethrough and help contain the liquid within the absorptive device, they also tend to be uncomfortable to wear. Accordingly, numerous prior art attempts have been made to provide breatheable backsheets for such absorptive devices, i.e., backsheets which are resistant to the passage of liquid moisture, but which are, at least to a degree, pervious to the passage of gases and vapors. The purpose of such prior art breatheable backsheets is to provide communication between the interior of the absorptive device and the exterior of the absorptive device, thus permitting evaporation of the absorbed liquids to the atmosphere and air circulation between the interior and exterior of the absorptive device.
Exemplary of such prior art absorptive devices employing breatheable backsheets are commonly assigned U.S. Pat. No. 3,989,867 issued to Sisson on Nov. 2, 1976; U.S. Pat. No. 3,156,242 issued to Crow, Jr on Nov. 10, 1964; U.S. Pat. No. 2,119,610 issued to Tasker on June 7, 1938; U.S. Pat. No. 3,439,678 issued to Thomas on Apr. 22, 1969; and commonly assigned U.S. Pat. No. 4,341,216 issued to Obenour on July 27, 1982, all of said patents being hereby incorporated herein by reference.
The aforementioned commonly assigned patent to Obenour discloses a disposable diaper provided with a two-element breatheable backsheet. The two elements are a vapor-pervious, relatively liquid-impervious outer sheet and a liquid-impervious inner panel. The inner panel is placed between the outer sheet and an absorbent core of the device in the crotch region of the disposable diaper. The relatively liquid-impervious outer panel disclosed by Obenour preferably comprises a polymeric film exhibiting a pattern of tapered capillaries as described in commonly assigned U.S. Pat. No. 3,929,135 issued to Thompson on Dec. 30, 1975. The outer panel is oriented in a direction such that the direction of relative liquid-impermeability is from the absorbent core to the exterior surface of the diaper. In the illustrated embodiment, this means that the apices of the tapered capillaries in the outer sheet are oriented in the direction of the absorbent core.
As with the earlier prior art structures, the primary thrust of Obenour is to permit breatheability between the moist absorptive core of the device and the atmosphere surrounding the exposed backsheet of the disposable diaper.
Because of the wide range of conditions experienced in use, absorbent devices of the prior art employing breatheable backsheets which permit limited communication between the absorptive element and the atmosphere surrounding the backsheet have not always functioned in the intended manner. For example, when such devices are subjected to higher than normal pressures due to movements or actions of the wearer, liquid may be discharged through the breatheable backsheet, thereby wetting the surrounding garments of the wearer.
An alternative prior art approach to improve wearer comfort yet preserve liquid impermeability between the absorptive element and the surrounding atmosphere has involved adding an additional wearer-contacting layer outside a moisture impermeable backing layer used to restrain the liquid. One such structure is disclosed in U.S. Pat. No. 4,200,103 issued to Black et al. on Apr. 29, 1980, which is hereby incorporated herein by reference.
The patent to Black et al. discloses an absorbent product for absorbing and retaining body fluids. It has a body facing side and a garment facing side and comprises an elongated, planar absorbent pad. The pad is enveloped in a generally rectangular, menstrual fluid-pervious wrapper with the longitudinal edges of the wrapper overlapping on the garment facing side of the product. A generally rectangular menstrual fluid-impervious barrier sheet is sandwiched between the wrapper and the pad. The barrier sheet overlies the garment facing side of the pad and at least the longitudinal side edges of the pad. At least two menstrual barrier seal lines are provided extending longitudinally with the product and sealing the longitudinal edge portions of the barrier sheet to the cover. The longitudinal seals are intended to prevent menstrual fluid from transferring, either by wicking or by seeping, across the seal line, while the fluid-impervious barrier sheet prevents strikethrough of any absorbed fluids. In a particularly preferred embodiment of the Black et al. invention a pocket is formed between the barrier sheet and the overlying wrapper. According to Black et al., the area in this pocket is open to free circulation of moisture vapor and air on both the inside and the outside surfaces of the wrapper, whereby perspiration deposited on the longitudinal edges of the pad can be evaporated and removed from the product before causing user skin irritation.
The fluid-pervious wrapper of Black et al., in a preferred embodiment, is comprised of a substantially planar fibrous material which, according to Black et al., is prevented from wicking menstrual fluid to the outermost surface of the pad by the longitudinal barrier seals. When the pad of Black et al. is subjected to pressure, the wearer's skin causes the outermost wrapper to make contact with the underlying fluid-impervious barrier layer. Thus, in situations where the wrapper is subjected to continuous pressure, the pocket formed between the wrapper and the barrier layer will be non-functional in those areas subject to the continuous pressure, i.e., any air circulation between that portion of the wearer's body applying the pressure and the barrier layer must be provided through the substantially planar wrapper material. If the substantially planar fibrous wrapper material disclosed by Black et al. does not provide sufficient separation between the wearer's skin and the barrier layer of the pad to permit significant air circulation to occur between the wearer's skin and the barrier layer, this may result in wearer perspiration at the interface, with consequent wearer discomfort.